The use of a ninhydrin as a colorimetric reagent for the detection and assay of amino acids, amines and peptides has been known in the art for nearly 60 years. It serves as the basis for the well known Stein-Moore procedure now extensively utilized in the automated assay of amino acids. McCaman and Robins described a fluorometric method for the detection of serum phenylalanine involving the reaction betwen ninhydrin and phenylalanine and discovered the fluorescence was greatly enhanced by the addition of a variety of peptides. Later, Udenfriend and coworkers, Anal. Biochem. 42, 222, 237 (1971), described a fluorometric assay procedure for primary amine-containing compounds, especially peptides and amino acids, which involved the reaction between the primary amine-containing compound, ninhydrin and an aldehyde, preferably phenylacetaldehyde. This procedure was shown to be much more efficient and sensitive than the Stein-Moore and McCaman-Robins procedures.